1. Field of the Invention
The present invention relates generally to the field of improved processes and systems for recovering fluid such as oil from earth formations. More particularly, this invention relates to a process and system to selectively inject pressurized gas into a plurality of interconnected wells for displacement of the liquid to be produced and to re-inject at least a portion of this gas into an adjacent well.
2. Description of the Prior Art
While the invention will be explained for purposes of simplicity with regard to its application to production of oil from oil bearing earth formations having little or no formation pressure, it is considered understood that the invention may be utilized effectively for displacement of other fluids that may or may not be located within earth formations. The present invention will be discussed in its application solely for the production of oil from oil bearing earth formations for purposes of simplicity and to facilitate ready understanding of the invention.
Various processes and systems have been developed in the past for recovering oil from subterranean formations which have insufficient formation pressure to cause the oil to flow. Such recovery methods in the past have taken the form of mechanically energized pumps and pneumatic displacement pumps. Recently, certain pneumatic displacement pumps have become available which utilize compressed air, steam, or natural gas to energize the pump. Oftentimes these pumps are designed such that the displacement or lift gas is not commingled with the fluid being produced, such as allowing the gas to bubble through the production fluid, but rather the lift gas is maintained in a separate system or chamber with the pump being actuated by simply allowing the lift gas to expand and thereby actuate the pump. Typical pumps are disclosed in U.S. Pat. Nos. 3,106,170; 3,797,968 and 3,873,238.
It has also been found that during operation of such pneumatic pumps, the lift gas which actuates the pump is not completely decompressed after pump actuation but rather remains at an elevated pressure capable of preforming additional work. However, in the past this gas has simply been recycled directly back to a gas source such as a conventional gas compressor without any attempt to take advantage of this remaining energy. Since it is common that this expended lift gas be collected in a central collection system and communicated to a central compressor, substantial portions of the energy contained in the compressed gas is dissipated while moving through this system. Therefore, substantial amounts of energy are lost through the failure of previously known systems to utilize at least a portion of the energy contained in the partially expended lift gas.
In recent years much emphasis has been placed upon the recovery of oil which heretofore has been uneconomical to produce. Typical of this previously uneconomical production is the highly viscous oil which often requires injection of steam or water in order to reduce the viscosity of the crude oil and thereby allow it to migrate toward a production well. Such operations are quite expensive and therefore it is necessary to make extensive efforts to maximize the efficiency of all artificial lift systems.
A feature of the present invention pertains to increasing overall efficiency of an artificial lift system utilized for producing closely spaced and interconnected wells.
Another feature of the present invention resides in its maximum utilization of available compressor capacity within an existing artificial lift system. A further feature of the present system involves the reduction in overall costs for lifting oil from oil bearing formations having insufficient pressure to cause the production fluid to flow.
It is also an important feature of the present invention to provide a novel gas injection and control system enabling increased cyclic injection and re-injection of pressurized lift gas without creating a need for additional compressor capacity.
The present invention is advantageous over the art in that the same is economical to construct, efficiently maximizes the amount of oil which may be produced with a limited amount of compressor capacity, and is easily controlled by a central controlling means.
The present invention is summarized in that an apparatus for utilizing pressurized gas for flowing liquid from a plurality of interconnected well includes an injection conduit connecting each of the wells to a central gas compression source, a lift control assembly for each of the wells which is connected to the injection conduit. A low pressure exhaust conduit is connected with each lift control assembly and communicates low pressure exhaust gas back to the gas source. A high pressure exhaust conduit is also connected to each lift control assembly and communicates high pressure exhaust gas capable of performing additional work to an adjacent well. This adjacent well is therefore pre-pressurized by the use of the high pressure exhaust lift gas from the prior well. Actuation of the pump in the adjacent well is then accomplished by increasing the pressure in the adjacent well an amount substantially less than what would have been required to actuate the pump without utilizing the high pressure exhaust.
Other features and advantages of the present invention will become apparent from the following description of the preferred embodiment when taken in conjunction with the accompanying drawing.